Seminar
Nanosecond Time-Resolved X-ray Crystallography
Professor Keith MoffatDepartment of Biochemistry and Molecular Biology
and
The Center for Advanced Radiation Sources
The University of Chicago
Monday, April 5, 1999
3:00 pm
3269 Beckman Institute
Structural changes accompany all chemical and biochemical reactions, and a full description of these structural changes is fundamental to an understanding of mechanism. They can occur very fast, and hence any spectroscopic, computational or structural technique that seeks to probe them must have excellent time resolution. The X-ray pulses that are emitted by third generation synchrotron sources such as the ESRF, APS and SPring8 are naturally polychromatic, very brief (with a duration around 100 ps and a repetition rate of hundreds of KHz) and sufficiently intense to yield a Lane X-ray diffraction pattern of good quality when they fall on a small, single crystal of a well-ordered macromolecule. If a structural reaction is initiated in the molecules in a crystal, for example by illumination with a laser pulse in the near UV-visible range, the subsequent time dependence of the X-ray structure amplitudes may be obtained with nansecond time resolution, and from them the time dependence of the space average structure in the crystal. It may finally be possible to extract the time-independent structures whose populations vary with time and contribute to this average.
